Can someone help me please?

I had been a teacher in the past. I used to teach groups almost 13 hours a day. one night, while standing up after using it,it seemed to me that my thinking is going out of my mind. I put my hand on the head and started calling my wife.All over the night, I went up the roof and down to get rid of these feelings but couldn�t. Anyhow I slept after sometime and when consulted the doctor, he asked me to relax and leave teaching. I relaxed for sometime and then started teaching to earn my livelihood but since that time, it is very difficult to study hard. What is the solution to get the same mental power please? now I remain confused and feel burdon in the middle of my mind(stressed?)